The present invention relates generally to apparatus for heating plastic preforms or parisons prior to blow molding containers, and particularly to apparatus for adjustably mounting heating lamps within an assembly such that a desired heating profile can be repeatedly obtained, and to apparatus for precisely measuring the position and alignment of the heating lamp mounting apparatus.
In many blow molding machines, a series of parisons are conveyed continuously along a defined path through an oven wherein heat is applied to the parisons from a battery of heating elements typically taking the form of linearly elongated infrared bulbs. Each bulb is arranged substantially horizontally and retained in position by clips which both hold the bulb at a desired position and connect the bulb to a source of electrical power. In some apparatus, the bulbs are situated at a fixed location and are not subject to repositioning. An example of such an apparatus is shown in FIG. 4 of U.S. Pat. No. 4,690,633.
It has been recognized that ovens for heating plastic preforms having heating lamps which are immovable makes the task of achieving a desired temperature profile throughout the body of the parisons very difficult. This is particularly true where the machine is used to mold a variety of containers from preforms of varying design. It has therefore been suggested to provide individual holders for each of the heating lamps which are independently movable with respect to each other toward and away from the path of the parisons. This linear adjustability is achieved by providing a plurality of shafts penetrating a wall of the preform oven, with a lamp being mounted on the inside end of the shaft. The outer end of the shaft includes a handle by which the position of the shaft can be manipulated from outside the oven while the oven is operating. An example of such an apparatus is disclosed in U.S. Pat. No. 4,923,395.
While this design for a linearly adjustable blow molding oven substantially enhances one's ability to adjust the temperature profile of parisons traveling through the oven, the design still does not achieve optimum temperature profile adjustment in all situations. Additionally, the exterior adjustability of the elements raises the likelihood of unauthorized changes to the temperature profile by machine operators not understanding the critical machine set-up or the desire to repeat exactly an earlier set-up.